My choice for greatest is Kevin Conroy, voice acting is harder than normal acting because you have to rely solely on your vocal performance to convey the characters emotions, you cannot rely on physical actions, facial expressions or anything else but your voice, and even with that Conroy managed to make me believe he was the best Batman and last for over a decade, granted he had advantages such as he didn't have to look the part or be the correct age. But then again, Keaton didn't look the part and was not the correct age but he managed to do a great job.
My vote for worse goes not to George Clooney but to Clark Batram. Before
I'm eaten alive let me explain. Think about it Clooney was a god-awful Batman, he made bad puns, his collection of deus ex machina gadgets would make Adam West envious, his costume included freakin' nipples and a coddpeice, and he wouldn't even change his voice for Batman. But most of those things were not his fault and the ones that were, I'm sure he could improve upon if he really wanted to. Now don't get me wrong, Clooney IMO would never make a good Batman, I actually believe he was the second worse. But, I also believe that if he tried he would be just a tad better than Batram, who only seems to get praised for his builld, everything else he gets praied for (costume, script) has nothing to do with him anyway, his acting was horrible
you need only pause the video at about 2:14 here to see what I mean
http://www.youtube.com/watch?v=67IU799GIL4
So I think if Clooney really tried he could be better than Batram, that is of corse assuming that the question "Greatest Batman" means who
could do the greatest job, if it means who
did the greater job it means I think they were both on par in terms of "suckiness", it also means I've wasted fifteen minutes of my life.